Tagging systems have been used for several years in identification and security applications. Conventional tagging systems generally include three basic components: a base transmitter; one or more identification tags; and a base receiver. The transmitter is used to generate and transmit an interrogation signal within an operating or interrogation zone. The identification tags, when present within the interrogation zone, respond to the interrogation signal by transmitting an identification signal. The identification signal transmitted from the tag is detected by the receiver and decoded to uniquely determine the identity of the tag.
While a number of applications that utilize tagging systems have emerged in the commercial market in recent years, conventional tagging systems employed in these applications have generally operated at low frequencies and utilize tags having dimensions equivalent to the size of a credit card or larger. In many applications, for example surveillance monitoring, the size of conventional tags present a disadvantage, as it is difficult to conceal the tags to prevent the detection of their presence. Conventional tag systems, with operating distances/zones of more than 12-18 inches, also utilize tags that require an active power source, such as a battery, which poses an additional disadvantage in security monitoring applications where the maintenance or replacement of the power source may present a problem.
In view of the above, it is an object of the invention to provide an identification/security tag system that utilizes miniaturized tags which can be readily concealed. It is a further object of the invention to provide an identification/security tag system that can be inexpensively implemented, and which preferably employs "passive" tags, that do not require a power source, or "semi-passive" tags, which do contain a power source, but that do not drain a substantial amount of power until an interrogation signal is detected.